For providing storage media of high density and large capacity, optical memory techniques using optical disks having pit-like patterns have been applied further to digital audio disks, video disks, text file disks, and further to data files or the like. In such an optical memory technique, information is recorded and reproduced with a high accuracy and reliability into an optical disk via a finely-converged optical beam. Such a recording-reproducing operation largely depends on the optical system, and particularly, reduction of the temperature characteristics is extremely important in the recording-reproducing operation. An optical head device is configured by assembling optical members such as a light source, a photodetector, a half-mirror and a lens into a predetermined frame. The respective optical members must be positioned precisely for preventing deviation of the optical axis or deviation of the focal point position.
For example, JP2000-266977A discloses a method of fixing a cylinder integrated lens in a frame. FIG. 7 is a perspective view showing a configuration of a conventional lens support mechanism. A sensor lens 17 is formed by PC-integrally casting a concave lens 31 as a main part of the optical members, a lens barrel 32 formed to surround the concave lens 31, and three support arms 33, 34 and 35 extending outward from the lens barrel 32. In the support arms 33 and 34, vertical slits 33a and 33b are formed respectively to extend from the tops to the bottoms so that the distal end portions will be deformed resiliently with respect to the proximal end portions.
FIG. 8 is a cross-sectional view showing a conventional lens support mechanism in an attached state. In FIG. 8, the center of the concave lens 31 is determined as an origin point where X-, Y- and Z-axes cross each other at right angles and the Z-axis conforms with the optical axis of the concave lens 31. A plane defined by the X- and Y-axes will be referred to as a first reference plane I, and a plane defined by the Y- and Z-axes will be referred to as a second reference plane II. A frame 18 for supporting the sensor lens 17 is formed with a first support surface 26 and a second support surface 27 both extending along the first reference plane I, and also a third support surface 28 extending along the second reference plane II.
This frame 18 has a groove 29 in which almost a half of the cross section of a lens barrel 32 is received in a non-contact fashion. One side face of each of the support arm 33 and the support arm 34 is in contact with the first support surface 26 and the second support surface 27 of the frame 18. One side face of the support arm 35 is in contact with the third support surface 28 of the frame 18. In this manner, the sensor lens 17 is attached to the frame 18.
The sensor lens 17 is urged, via a leaf spring 36 fixed to the frame 18 as a resilient securing means, in a composite direction between the X-axis and the Y-axis as shown with a dotted arrow in FIG. 8. The distal ends of the support arms 33 and 34 are firmly fixed onto the respective support surfaces 26 and 27 of the frame 18 via adhesives 37 and 38 so as not to fall off the frame 18.
In the thus configured sensor lens 17, the support arms 33 and 34 are pressed resiliently via the leaf spring 36 against the support surfaces 26 and 27, and the support arm 35 is pressed resiliently against the support surface 28. In this manner, the center of the sensor lens 17 is fixed at the optical axis position.
FIG. 9 is a schematic view for explaining operations of a conventional lens support mechanism. As shown in FIG. 9, when the concave lens 31 and the lens barrel 32 thermally expand, the proximal end portions of the support arms 33 and 34 are shifted along the support surfaces 26 and 27, and the support arm 35 is shifted along the support surface 28. Since the distal end portions of the support arms 33 and 34 are fixed respectively at the support surfaces 26 and 27 by means of the adhesives 37 and 38, the displacement of the proximal end portions of the support arms 33 and 34 can be accommodated by the vertical slits 33a and 33b. In this case, the optical axis of the concave lens 31 does not change in position because the thermal expansion occurs only in a radial direction from the center of the lens 31.
As shown in FIG. 9, the distal end portions of the support arms 33 and 34 are fixed with the adhesives 37 and 38, and the center of the concave lens 31 is separated along the optical axis direction by a distance d from the position fixed by means of the adhesives 37 and 38. Therefore, the position of the concave lens 31 will be displaced along the optical axis direction by ‘a distance (d)’×‘coefficient of thermal expansion’×‘ΔTm (temperature difference)’ due to expansion and contraction caused by heat. Thus, the temperature characteristics of the entire optical pickup device can be improved further by intentionally creating a deviation in advance that can accommodate a deviation in the optical axis direction caused by expansion and contraction by heat of the other components such as a half-mirror, a collimator lens and an objective lens.
In an optical head device, it is required to assure an operation environment in a wide temperature range from a low temperature to a high temperature. In particular, temperature characteristics must be improved in order to prevent the collimator lens from defocusing with respect to the semiconductor laser. Since the optical head enclosure supporting the collimator lens expands due to temperature changes and since the stem expands in an area ranging from a laser attachment reference surface to an emission point, a displacement occurs between the emission point and the collimator lens. Furthermore, a back focus amount of the collimator lens will vary due to a change in oscillation wavelength of a laser diode and also changes in the refractive index and shape of the collimator lens.
However, since a light beam passing through the collimator lens will not become a parallel light beam due to the influences, a beam spot on the optical disk will be defocused.
In the above-described lens support mechanism, since a lens integrated with a lens barrel is fixed directly to a frame with an adhesive, the distance d along the optical axis direction cannot be determined quantitatively because of varying amount of the adhesives and varying positions for adhesion. This results in a problem that a deviation along an optical axis direction, which is caused by thermal expansion and contraction, cannot be accommodated quantitatively.
Furthermore, the lens integrated with a lens barrel has a complicated structure, and thus the production cost is increased and a further precise adjustment is required. As a result, an optical head device including the lens support mechanism of this lens integrated with a lens barrel and also an optical information device have problems of degradation of the temperature characteristics and high cost.
An object of the present invention is to provide a lens support mechanism that can accommodate displacement between an emission point and a collimator lens, which is caused by thermal expansion and thermal contraction, and provides also an optical head device and an optical information processor.